Notes
Fungi Overview
Sections
- Kingdom: Fungi
- Eukaryotic
- Rigid cell walls that comprise chitin and glucan.
- Cell membranes contain the sterol erogsterol, which is the target of some antifungal drugs.
Fungal Forms
Unicellular fungi are often referred to as yeast.
Multicellular forms are often referred to as filamentous or mold forms.
Dimorphic: many species exist as both mold and yeast forms, depending on environmental conditions such as temperature, carbon dioxide concentration, and pH.
Reproduction
Fungi use a variety of strategies for reproduction.
Can reproduce sexually or asexually, and some species are capable of both.
Mechanisms of reproduction also vary, and include the production of spores and budding.
Infection
Mycoses are fungal diseases.
Most fungi are opportunistic pathogens, rather than primary pathogens, because they lack the ability to breach the host's protective barriers.
Important exceptions cause primary respiratory infections that can disseminate within the host.
Includes some ascomycetes and endemic dimorphic fungi.
Mycotoxins are toxins produced by fungi - they cause mycotoxicoses.
Not all mycotoxins are harmful to humans – we use mycotoxins that are toxic to bacteria to create antibiotics, such as penicillin!
Fungal Cell Structure
Typical fungal cell
Outer cell wall comprises chitin and glucan; chitin provides rigidity.
Cell membrane comprises erogsterol in place of the cholesterol found in our cell membranes.
Nucleus, mitochondria, Golgi, and endoplasmic reticulum.
Fungi morphology
Fungi take on a range of shapes, from ovoid to filamentous.
A given population of fungi may appear as a mixture of morphological types.
The filamentous forms grow via elongation, while the unicellular forms replicate via budding or fission.
The filamentous form can invade host tissues.
Filamentous forms: Hyphae & Pseudohyphae
Hyphae appear as smooth branching filaments:
May be septated or coenocytic (non-septated).
Septa may have pores for materials to move within the filament.
Mycelium is a mass of hyphae.
These can be visible to the eye, and are commonly referred to as "mold."
Pseudohyphae look similar to hyphae, but comprise chains of cells with constriction at the septal junctions.
A mass of pseudohyphae is sometimes referred to as a pseudomycelium.
The differences between hyphae and pseudohyphae can be difficult to distinguish.
Unicellular forms: Yeast
Appear as ovoid or round.
They replicate via budding or fission, and form discrete, separate cells.
Notice that we've identified individual cells within the same sample as the pseudohyphae.
Cell (aka, yeast)-to-pseudophyhae transition
Individual fungal cell develops an outgrowth, which is called the "germ tube."
The germ tube ultimately becomes a chain of cells that remain attached to one another at septa.
As mentioned earlier, some fungi species undergo this transition in response to environmental conditions.
Mycoses
Superficial and cutaneous mycoses
Infect skin, hair, and nails.
A common example of a superficial mycosis is ringworm (aka, Tinea or Dermatophytosis).
Subcutaneous mycoses
Localized, chronic infections that produce abscesses, ulcers, or sinuses with drainage tracts.
An example of a subcutaneous mycosis is Maduromycosis, in which fungal tumors invade deeper tissues.
Endemic, aka, systemic, mycoses
Begin as primary infections in the lungs that disseminate through the body.
An example of an endemic mycosis is histoplasmosis.
Opportunistic mycoses
Caused by fungi that are found in the human microbiome or commonly in the environment.
Disease is typically limited to individuals with immunosuppression, prosthetic devices, or underlying disease.
Aspergillosis is an important example of an opportunistic fungal mycosis.
Fungi Nomenclature
Until recently, members of Ascomycota and Basidiomycota had dual nomenclature because they were capable of producing both sexual and asexual spores.
The form of a species that produces asexual spores is the anamorph, and would be given one name.
The form of a species that produces sexual spores is the teleomorph, and would be given a different name.
While the distinction can be important in clinical and laboratory settings, the dual naming system also created confusion for many. In our tutorials, we will focus on the forms of medical importance.
References
"A Resident's Fungal Morphology." Accessed September 17, 2018. http://labmed.ucsf.edu/education/residency/fung_morph/fungal_site/page1.01.html.
Bennett, J. W., and M. Klich. "Mycotoxins." Clinical Microbiology Reviews 16, no. 3 (July 2003): 497–516. https://doi.org/10.1128/CMR.16.3.497-516.2003.
"Characteristics of Fungi | Boundless Biology." Accessed September 18, 2018. https://courses.lumenlearning.com/boundless-biology/chapter/characteristics-of-fungi/.
Kasper, Dennis L., Stephen Hauser L., Larry Jameson J., Anthony S. Fauci, Dan Longo L., and Joseph Loscalzo. Harrison's Principles of Internal Medicine. 19th ed. McGraw-Hill Education, 2015.
Levinson, W. Review of Medical Microbiology & Immunology. 14th ed. McGraw-Hill Education, 2016.
Madhani, Hiten D, and Gerald R Fink. "The Control of Filamentous Differentiation and Virulence in Fungi." Trends in Cell Biology 8, no. 9 (September 1998): 348–53. https://doi.org/10.1016/S0962-8924(98)01298-7.
McGinnis, Michael R., and Stephen K. Tyring. "Introduction to Mycology." In Medical Microbiology, edited by Samuel Baron, 4th ed. Galveston (TX): University of Texas Medical Branch at Galveston, 1996. http://www.ncbi.nlm.nih.gov/books/NBK8125/.
Murray, P. R., Rosenthal K.S., & Pfaller, M.A. Medical Microbiology. 8th ed. Elsevier, 2016.
Nantel, André, Daniel Dignard, Catherine Bachewich, Doreen Harcus, Anne Marcil, Anne-Pascale Bouin, Christoph W. Sensen, et al. "Transcription Profiling of Candida Albicans Cells Undergoing the Yeast-to-Hyphal Transition." Molecular Biology of the Cell 13, no. 10 (October 2002): 3452–65. https://doi.org/10.1091/mbc.E02-05-0272.
"Phenotypic Switching in Fungi." Accessed September 19, 2018. https://www-ncbi-nlm-nih-gov.proxy.medlib.uits.iu.edu/pmc/articles/PMC2746697/.
Singh, Vivek Kumar, Mukesh Meena, Andleeb Zehra, Arti Tiwari, Manish Kumar Dubey, and R. S. Upadhyay. "Fungal Toxins and Their Impact on Living Systems." In Microbial Diversity and Biotechnology in Food Security, edited by R.N. Kharwar, R.S. Upadhyay, N.K. Dubey, and Richa Raghuwanshi, 513–30. New Delhi: Springer India, 2014. https://doi.org/10.1007/978-81-322-1801-2_47.
Sudbery, Peter E. "The Germ Tubes of Candida Albicans Hyphae and Pseudohyphae Show Different Patterns of Septin Ring Localization." Molecular Microbiology 41, no. 1 (July 1, 2001): 19–31. https://doi.org/10.1046/j.1365-2958.2001.02459.x.
https://doi.org/10.1046/j.1365-2958.2001.02459.x.
Sudbery, Peter, Neil Gow, and Judith Berman. "The Distinct Morphogenic States of Candida Albicans." Trends in Microbiology 12, no. 7 (July 1, 2004): 317–24. https://doi.org/10.1016/j.tim.2004.05.008.
"Superficial (Cutaneous) Mycoses." Accessed September 18, 2018. http://www.microbiologybook.org/mycology/mycology-4.htm.
Images:
Blaylock, Bob. English: Mold, Growing in a Petri Dish from a Sample of Dust and Debris from Some Repair Work in the Bathroom of Our Apartment. August 15, 2010. Own work. https://commons.wikimedia.org/wiki/File:20100815_1818_Mold.jpg.
Hille, Rob. Latina: Agaricus BisporusLatina: Mycelium. December 9, 2011. Own work. https://commons.wikimedia.org/wiki/File:Mycelium_RH_(3).jpg.
Kellner, Tobi. English: Oyster Mushroom (Pleurotus Ostreatus) Mycelium Growing in a Petri
Dish on Coffee GroundsDeutsch: Austernpilz Myzel (Pleurotus Ostreatus) in Einer Petrischale Auf Kaffeesatz. February 10, 2012. Own work. https://commons.wikimedia.org/wiki/File:Oyster_mushroom_(Pleurotus_ostreatus)_mycelium_in_petri_dish_on_coffee_grounds.JPG
Tashkoskip. Македонски: (Горе) December 12, 2015. Own work. https://commons.wikimedia.org/wiki/File:Mycelium_and_hyphae_of_the_fungus_Rhizoctonia_solani.jpg.